Electrodes are used to provide electrical stimulation, including electrical stimulation of neural structures in patients suffering from chronic pain. A variety of electrodes and electrode arrays exist for operation in conjunction with a pulse generator. U.S. Patent Application Publication No. 2006/0136008, incorporated herein by reference in its entirety, discloses a number of electrode arrays. For example, and referring to FIG. 1A, an electrode array 10 known in the prior art is shown. The electrode array 10 includes a plurality of electrodes or contacts 14 located at the distal region 18 of a lead 22. Referring to FIG. 1B, an electrode array 10 is located within an electrode paddle 26. The electrode array 10 is formed of a plurality of contacts 14 situated within the relatively flat electrode paddle 26. Referring now to FIG. 1C, two electrode arrays 10 are located within two electrode paddles 26, wherein the leads 22 extend to a common junction 30, and wherein the leads 22 are controlled by a common pulse generator (not shown). For the electrode array shown in FIG. 1C, each electrode array 10 is formed of a plurality of contacts 14 situated within the relatively flat electrode paddle 26.
For the above noted electrode arrays, the electrical lead 22 conveys a pulse of electrical energy from a pulse generator to the electrode arrays 10. In general, the lead 22 enters the electrode array 10 or paddle 26 at a proximal end 34 of the electrode array 10 or paddle 26, where the distal end 38 of the lead 22 is co-planar with the electrode array 10 or paddle 26.
The structure of the existing electrode arrays presents difficulties for a surgeon implanting the electrode paddles within certain areas of the spine because the anatomy of the spine does not necessarily lend itself to implanting an electrode array directly onto the nerves of the spine when the distal end 38 of the lead 22 is also coplanar with the electrode array 10. That is, the spine is three dimensional, and an electrode array 10 cannot necessarily be properly positioned within the spinal canal and on the target neural structures of the spine when the distal end 38 of the electrical lead 22 extends in a coplanar orientation with the electrode paddle 26 containing the electrode array 10.
Referring now to FIG. 1D, a partial side view of an electrode paddle 42 of the prior art is shown implanted at the cervical vertebrae C1-C2 level, and in FIG. 1E, a posterior view of the electrode paddle 42 is shown. For this typical implant configuration, the electrode lead 22 extends from a longitudinal end of the electrode paddle 42 in a caudal direction between the occipital bone and C1. As shown in FIG. 1F, in extension the occipital bone forces the electrode lead 22 downward and pinches the electrode lead 22 against the C1. With repeated motion, the electrode lead 22 experiences stress that can be detrimental to the structural integrity of the electrode wire 22 and its connection to the electrode paddle 42.
To address the spatial limitations resulting from the implant target location and the existing electrode paddle geometries, the surgeon may be forced to compromise in some fashion, such as by: (1) using an alternate and less attractive array configuration; (2) positioning the electrode array near the target location but not exactly at the desired target location; and/or (3) allowing the spine to bend the distal end of the electrical lead at the proximal end of the electrode paddle, thereby risking the structural integrity of the lead connection to the electrode paddle. Thus, it would be advantageous to provide an electrical paddle having an electrical lead configuration that more appropriately accommodates the anatomical features of the spine.
U.S. Pat. No. 3,724,467, incorporated herein by reference in its entirety, discloses an electrode paddle having a lead connection that enters the paddle at an angle of between 15 to 45 degrees. However, this reference fails to disclose a lead connection that connects to the body portion of the electrode paddle along a steep inclination, such as along a substantially perpendicular alignment. Such a perpendicular alignment would be advantageous for implanting at the opening between the L5-S vertebrae.
With regard to use of electrodes to relieve pain, foot pain is notoriously difficult to treat with intraspinal stimulation. If the electrode(s) are placed at the spinal cord level, the stimulation eventually goes away from the foot area because other larger nerve fibers (mostly the thigh) eventually end up capturing most of the stimulation. In order to maintain the stimulation in the foot area, the most precise and reliable target is the L4, L5, S1, S2 nerve roots at the L4-L5 spine level. Electrodes placed on these nerve roots will generally maintain stimulation in the foot. There are several issues with stimulation of the lumbar nerve roots for pain. The target nerves are the lumbar dorsal (sensory) roots that carry sensation. Stimulation of the ventral (motor) roots, which are adjacent of the sensory roots, is greatly undesirable because it produces motor contractions. If an electrode is placed under the lamina, as is necessary with the existing shaped paddle leads, it will exert some degree of pressure on the nerve roots, even if minimal. This amount of pressure is often enough to squeeze the dorsal roots very close to the ventral roots. A significant side effect of the nerve roots coming closer together is that the stimulation will almost inevitably result in stimulating the motor roots preferentially, thereby negating the beneficial effects of the stimulation.
In order to avoid activation of the motor roots, a minimal amount of compression, if any, must be exerted on the nerve roots. In order to accomplish this, no bone should be present dorsal to the electrodes placed on the nerve roots. This presents a difficulty because the existing commercially-available paddle leads rely on the presence of bone dorsally to maintain them in place and prevent their displacement.
Another area that has been problematic for electrode placement is the C1-C2 region of the spine. This area of the spinal cord is an excellent target for stimulation since all of the nerve fibers coming from the upper and lower extremities converge at the C1-C2 level. A physician might, therefore, have the possibility to stimulate all four extremities from one single target. However, two issues make that placement less than ideal with the currently available electrodes. First, since the electrode(s) are placed entering the spine between the occiput and the arch of C1, they are subjected to a significant amount of motion. More particularly, the cranio-cervical junction has one of the highest motion of any spine segment. This puts the electrode at a very high risk of fracturing or possible malfunction. Secondly, the C2 lamina is relatively thick and tends to push the electrode closer to the spinal cord. As a result, the stimulation current more easily spreads, not only to the dorsal columns (a desirable effect), but also to the motor fibers. This will result in undesirable motor contractions that might negate the beneficial effects of the stimulation. Even a thinner electrode might not obviate that problem. Accordingly, the best solution is to have the electrode placed in an area where little or no bone will be present to exert pressure on the electrode.
Yet another area of interest is the T7-T8-T9-T10-T11 area, where a physician may be trying to achieve stimulation of the dorsal columns affecting the lower extremities and the axial lumbar area (which is notoriously difficult to stimulate). Stimulation of the nerves in the T7-T8-T9-T10-T11 levels is often performed to treat pain in the lower back and in the lower extremities. Here again, the configuration of the vertebrae and the location of the target neural structures do not necessarily facilitate ease of treatment using existing commercially-available electrodes.
In addition, while existing electrodes paddles include some material along the boundary of the paddle, the existing electrode paddles do not necessarily include sufficient material for allowing the electrode paddle to be anchored or otherwise stabilized within the environment of the spinal canal. Thus, it would be advantageous to provide an electrode paddle that has structure for allowing the electrode paddle to cooperate with the structure of the vertebrae of the spine for maintaining the position of the electrode paddle within the spinal canal once it is implanted, whether or not a laminectomy has been performed.
Another difficulty associated with electrode arrays and electrode paddles of the prior art is that they are generally provided in a one-piece configuration and do not readily permit the surgeon to modify their shape to accommodate the physical attributes of the patient during surgery. Accordingly, it would be advantageous to provide an electrode paddle that accommodated modification during the surgical procedure to allow the surgeon to modify the shape and/or orientation of the electrode array to suit the patient's needs.